Methods for depositing thin films comprising indium nitride by atomic layer deposition

ABSTRACT

Atomic layer deposition (ALD) processes for forming thin films comprising InN are provided. The thin films may find use, for example, in light-emitting diodes.

REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119(e) to U.S.provisional application No. 61/504,985, filed Jul. 6, 2011, thedisclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present application relates generally to methods and compounds forforming thin films comprising indium nitride (InN) by atomic layerdeposition. Such films may find use, for example, in optoelectronicapplications, such as light emitting diodes (LEDs).

Description of the Related Art

Currently several issues plague the manufacturing of InN and GaN-basedLEDs: poor yield of devices producing the desired wavelength andsubsequent need for cumbersome device sorting, and decreasing revenueper substrate (the price ratio of LEDs producing the desired wavelengthand ones with a slight deviation from this wavelength is roughly 500:1).Currently an InGaN/GaN multi-quantum well (MQW) structure in HB-LEDs isdeposited by MOCVD and the deposition involves thermal cycling betweenapproximately 700° C. and 950° C. The high temperature used limits, dueto diffusion, the maximum indium concentration in the InGaN; in practicethe indium concentration is limited roughly to 20 atom-% beforesignificant diffusion of indium occurs. Additionally, in the MOCVDdeposited HBLED, small variations in the deposition temperature insidethe substrate area lead to minute changes in indium concentration in theInGaN layer and, subsequently, a change in the emission wavelength,leading to poor yield due to poor indium uniformity in indium content inInGaN. MOCVD also has limitations in maximum obtainable indiumconcentration in InGaN, limited earlier by increased mobility due tothermal cycling. thermal budget, and temperature uniformityrequirements.

A need exists, therefore, for methods for controllably and reliablyforming thin films comprising InN by ALD.

SUMMARY OF THE INVENTION

The methods disclosed herein provide reliable atomic layer deposition(ALD) methods for forming thin films comprising InN. The thin films canbe used, for example, in quantum well structures, LEDs and lasers. Thefilms can be doped, for example with one or more of Ga, Al, Mg, P orother dopants.

In accordance with one aspect of the present invention, atomic layerdeposition (ALD) processes for forming an InN containing thin film on asubstrate in a reaction chamber are provided. The processes typicallycomprise a plurality of deposition cycles, each cycle comprising:providing a pulse of a first vapor phase In reactant into the reactionchamber to form no more than about a single molecular layer of the Inreactant on the substrate; removing excess first reactant from thereaction chamber; providing a pulse of a second vapor phase reactantcomprising N to the reaction chamber such that the second vapor phasereactant reacts with the In reactant on the substrate to form an InNcontaining thin film; and removing excess second reactant and reactionbyproducts, if any, from the reaction chamber. In some embodiments thereaction chamber is part of a flow-type reactor. In some embodiments thethin film is an epitaxial or single crystal film. The growth rate of thethin film may be less than about 2 angstroms/cycle, less than about 1.5angstroms/cycle, less than about 1 angstrom/cycle, less than about 0.5angstrom/cycle or even less than about 0.3 angstrom/cycle depending onthe reaction conditions.

In some embodiments, a thermal ALD process is used to deposit an InNcontaining thin film. The In reactant may be an In halide, such as InCl₃or InI₃ and the second reactant may be a nitrogen containing reactantsuch as NH₃ or N₂H₄. The temperature of the process is preferably belowabout 800° C., below about 700° C., below about 600° C., below about500° C. or below about 400° C. The reaction chamber may be part of aflow-type reactor. In some embodiments the deposited film is anepitaxial or single-crystal film.

In other embodiments, a thermal ALD process uses an organic Inprecursor, such as cyclopentadienylindium (InCp), dimethylethylindium(DMEI), trimethylindium (TMI) or triethylindium (TEI). In someembodiments, the organic In precursor has the formula InR₃, wherein theR is selected from the group consisting of substituted, branched, linearand cyclic C1-C10 hydrocarbons. The second reactant may be a nitrogencontaining reactant such as NH₃ or N₂H₄. The temperature of the processis preferably selected such that the In reactant does not decompose, forexample below about 400° C. or below about 300° C., depending on theparticular reactant employed. The reaction chamber may be part of aflow-type reactor. In some embodiments the deposited film is anepitaxial or single-crystal film.

In other embodiments, a plasma ALD process is used to deposit an InNcontaining thin film. In some such embodiments, the In precursor may be,for example, an In halide precursor, such as InCl₃ or InI₃. The secondreactant comprising N may be a nitrogen plasma containing precursor. Insome embodiments the nitrogen plasma is generated in situ, for exampleabove or directly in view of the substrate. In other embodiments thenitrogen plasma is formed remotely, for example upstream of thesubstrate or upstream of the reaction chamber in which the substrate ishoused. In some such embodiments, the nitrogen plasma does not have asubstantial amount of N ions, and is primarily N atoms. In someembodiments the second reactant also comprises hydrogen plasma. In someembodiments the second reactant is a mixture of H₂/N₂ plasma. In someembodiments the second reactant is a nitrogen and hydrogen containingplasma created from H₂/N₂ gas mixture, which preferably has an H₂:N₂ratio above 3:1, more preferably above 4:1 and most preferably above5:1. In some cases H₂:N₂ ratios from about 5:1 to about 10:1 can beused. The reaction temperature may be, for example, less than about 500°C., less than about 400° C., less than about 300° C. or even less thanabout 200° C. In some cases the reaction temperature is less than about100° C. The process may be performed in a flow-type reactor. In someembodiments the deposited film is an epitaxial or single-crystal film.

In other plasma ALD processes an organic In reactant is used, such asdimethylethylindium (DMEI), trimethylindium (TMI) or triethylindium(TEI). In some embodiments, the organic In precursor has the formulaInR₃, wherein the R is selected from the group consisting ofsubstituted, branched, linear and cyclic C1-C10 hydrocarbons. In someembodiments the In precursor is not an In-halide, such as InCl₃. Thesecond reactant comprising N may be a nitrogen plasma containingprecursor. In some embodiments the nitrogen plasma is generated in situ,for example above or directly in view of the substrate. In otherembodiments the nitrogen plasma is formed remotely, for example upstreamof the substrate. In some such embodiments, the nitrogen plasma does nothave a substantial amount of N ions, and is primarily N atoms. In someembodiments the second reactant also comprises hydrogen plasma. In someembodiments the second reactant also comprises ammonia (NH₃) plasma. Insome embodiments the second reactant is a mixture of H₂/N₂ plasma. Insome embodiments the second reactant is a nitrogen and hydrogencontaining plasma created from H₂/N₂ gas mixture which preferably has aH₂:N₂ ratio above 3:1, more preferably above 4:1 and most preferablyabove 5:1. In some embodiments H₂:N₂ ratios from about 5:1 to about 10:1can be used. In some embodiments the second reactant is a nitrogen andhydrogen containing plasma created from H₂/N₂ gas mixture whichpreferably has a H₂:N₂ ratio below 3:1, more preferably below 5:2 andmost preferably below 5:4. In some embodiments H₂:N₂ ratios from about1:4 to about 1:2 can be used. The reaction temperature is generallychosen such that the In precursor does not decompose and may be, forexample, less than about 400° C., less than about 300° C. or even lessthan about 200° C., depending on the precursor. The process may beperformed in a flow-type reactor. In some embodiments the deposited filmis an epitaxial or single-crystal film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a flow chart generally illustrating a method for forming anInN film in accordance with some embodiments;

FIG. 1B is a flow chart generally illustrating a method for forming aGaN film in accordance with some embodiments;

FIG. 2A is a graph showing the growth rate versus InN/(InN+GaN) cycleratio in accordance with one embodiment;

FIG. 2B is a graph showing In/(In+Ga) ratio versus InN/(InN+GaN) cycleratio in accordance with one embodiment;

FIG. 3A is a graph showing the thickness of deposited InGaN films versushydrogen/nitrogen ratio in accordance with one embodiment;

FIG. 3B is a graph showing the roughness of deposited InGaN films versushydrogen/nitrogen ratio in accordance with one embodiment;

FIG. 3C is a graph showing the density of deposited InGaN films versushydrogen/nitrogen ratio in accordance with one embodiment;

FIG. 4A is a graph showing the thickness of deposited InGaN films versusplasma power in accordance with one embodiment;

FIG. 4B is a graph showing the roughness of deposited InGaN films versusplasma power in accordance with one embodiment;

FIG. 4C is a graph showing the density of deposited InGaN films versusplasma power in accordance with one embodiment;

FIG. 5 is a graph showing the growth rate per cycle versus galliumreactant supply as represented by turns of the valve supplying thegallium reactant in accordance with one embodiment;

FIG. 6A is a glancing incidence x-ray diffraction (GIXRD) graph of aInGaN film deposited on sapphire in accordance with one embodiment;

FIG. 6B is a glancing incidence x-ray diffraction (GIXRD) graph of a GaNfilm deposited on sapphire in accordance with one embodiment;

FIG. 6C is a glancing incidence x-ray diffraction (GIXRD) graph of aInGaN film deposited on sapphire in accordance with one embodiment;

FIG. 7 is an x-ray diffraction graph of a InGaN film deposited onsapphire heat treated at various temperatures in accordance with oneembodiment;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As discussed above, InN-containing films find use in a variety ofapplications, including p quantum well structures, LEDs and lasers. Thefilms can be doped additionally with Ga, Al, Mg, P or other dopants.

Deposition of indium containing thin films, such as indium oxides, byusing chemical deposition methods like CVD or ALD has been moredifficult than in the case of gallium deposition. Fewer suitable (forexample volatile enough) indium precursors have been available for vapordeposition methods. For example in current LED processing, deposition ofIn-containing thin films of sufficient quality has been more difficultthan GaN deposition. Embodiments herein can be used to reliably depositInN thin films, for example achieving controlled composition throughoutInN films and doped InN and GaN films or nanolaminate films.

While the embodiments of the present invention are discussed in thegeneral context of high brightness LEDs (HB-LEDs), the skilled artisanwill appreciate that the principles and advantages taught herein willhave application to other devices and applications. Furthermore, while anumber of processes are disclosed herein, one of ordinary skill in theart will recognize the utility of certain of the disclosed steps in theprocesses, even in the absence of some of the other disclosed steps, andsimilarly that subsequent, prior and intervening steps can be added.

InN containing films, including those doped with Ga, Al, Mg, P or otherdopants, can be deposited on a substrate by atomic layer deposition(ALD) type processes. ALD type processes are based on controlled,self-limiting surface reactions of precursor chemicals. Gas phasereactions are avoided by feeding the precursors alternately andsequentially into the reaction chamber. Vapor phase reactants areseparated from each other in the reaction chamber, for example, byremoving excess reactants and/or reactant byproducts from the reactionchamber between reactant pulses.

Briefly, a substrate is loaded into a reaction chamber and is heated toa suitable deposition temperature, generally at lowered pressure. Insome embodiments the reaction chamber is part of a flow-type reactor.Thus, in some embodiments reactants flow from an inlet, over thesubstrate and to a separate outlet. Reactants may be provided with theaid of a carrier gas, preferably an inert carrier gas or a mixture ofgases (Ar+H₂ for example).

Examples of suitable reactors that may be used include commerciallyavailable ALD equipment such as the F-120® reactor, Pulsar® reactor andAdvance® 400 Series reactor, EmerALD available from ASM America, Inc ofPhoenix, Ariz. and ASM Europe B.V., Almere, Netherlands. In addition tothese ALD reactors, many other kinds of reactors capable of ALD growthof thin films, including CVD reactors equipped with appropriateequipment and means for pulsing the precursors can be employed.Preferably, reactants are kept separate until reaching the reactionchamber, such that shared lines for the precursors are minimized.

The growth processes can optionally be carried out in a reactor orreaction space connected to a cluster tool. In a cluster tool, becauseeach reaction space is dedicated to one type of process, the temperatureof the reaction space in each module can be kept constant, whichimproves the throughput compared to a reactor in which the substrate isheated up to the process temperature before each run.

A stand-alone reactor can be equipped with a load-lock. In that case, itis not necessary to cool down the reaction space between each run.

In embodiments in which at least one of the reactants comprise a plasmareactant (a plasma-enhanced ALD or PEALD process), the plasma may begenerated in situ, that is above or in direct line of sight of thesubstrate. In other embodiments the plasma is generated remotely,upstream of the substrate or upstream of the chamber housing thesubstrate during deposition.

Deposition temperatures are typically maintained below the thermaldecomposition temperature of the reactants but at a high enough level toavoid condensation of reactants and to provide the activation energy forthe desired surface reactions. Of course, the appropriate temperaturewindow for any given ALD reaction will depend upon a variety of factorsincluding the surface termination and reactant species involved. Here,the temperature varies depending on the type of film being deposited andthe nature of the reactants. The temperature is preferably at or belowabout 800° C. for thermal ALD processes, more preferably at or belowabout 400° C. For processes that use plasma, the deposition temperatureis preferably at or below about 400° C., more preferably at or belowabout 200° C. and in some cases even below about 100° C.

In some embodiments InN is formed using an InN deposition cycle in whicha substrate is alternately and sequentially contacted with an Inprecursor and a N precursor. The InN deposition methods described hereincan be thermal ALD, plasma ALD, or a combination of thermal and plasmaALD, as discussed below. FIG. 1A is a flow chart generally illustratinga method for forming an InN film in accordance with some embodiments.The substrate is contacted with an In precursor 100 followed by removingany excess reactant 110. The substrate is then contacted with a nitrogenprecursor 120 followed by removing any excess reactant 130. The stepsare repeated until a film of a desired thickness is formed 140.

In some embodiments, in an InN deposition cycle a first In reactant isconducted or pulsed into the chamber in the form of a vapor phase pulseand contacted with the surface of the substrate. Conditions arepreferably selected such that no more than about one monolayer of thefirst In reactant is adsorbed on the substrate surface in aself-limiting manner. The appropriate pulsing times can be readilydetermined by the skilled artisan based on the particular circumstances.In some embodiments, pulsing times are from about 0.05 to 10 seconds. Insome embodiments the pulsing times are from about 0.05 s to about 1.0 s,preferably from about 0.1 s to about 0.5 s, more preferably from about0.1 s to about 0.3 s.

In some embodiments the In reactant is an In halide, such as InCl₃ orInI₃. In other embodiments the In reactant may be an organic indiumprecursor, including a (metal)organic or organometallic In precursor.Exemplary precursors include cyclopentadienylindium (InCp),dimethylethylindium (DMEI), trimethylindium (TMI) or triethylindium(TEI). In some embodiments, the organic In precursor may have theformula InR₃, wherein the R is selected from substituted, branched,linear or cyclic C1-C10 hydrocarbons. In some embodiments 0-3 of the Rgroups are methyl and the rest are ethyl. In some embodiments, the Inprecursor may be, for example, an In halide precursor, such as InCl₃ orInI₃. In some embodiments, the In precursors has both a halide ligandand organic ligand, for example InR_(x)X_(3-x), wherein x is from 1 to 2and R is organic ligand, such as alkyl or alkenyl and X is halide, suchas chloride. Examples of this kind of In precursors might be, forexample, dimethylindiumchloride (CH₃)₂InCl. The precursors can be usedin both thermal and plasma ALD processes.

In some embodiments the In precursor is not an In-halide, such as InCl₃.

Excess first reactant and reaction byproducts, if any, are removed fromthe reaction chamber, such as by purging with an inert gas. Purging thereaction chamber means that vapor phase precursors and/or vapor phasebyproducts are removed from the reaction chamber such as by evacuatingthe chamber with a vacuum pump and/or by replacing the gas inside thereactor with an inert gas such as argon or nitrogen. Typical purgingtimes are from about 0.05 to 20 seconds, more preferably between about 1and 10, and still more preferably between about 1 and 2 seconds.However, other purge times can be utilized if necessary, such as wherehighly conformal step coverage over extremely high aspect ratiostructures or other structures with complex surface morphology isneeded.

A second gaseous reactant comprising N is pulsed into the chamber whereit reacts with the first In reactant bound to the surface. The nitrogenprecursor may be, for example, NH₃ or N₂H₄. In some embodiments the Nprecursor does not comprise an activated compound. However, in someembodiments the N precursor comprises nitrogen plasma. In someembodiments the nitrogen plasma is generated remotely and comprisesprimarily N atoms and does not comprise a substantial amount of N ionswhen it reaches the substrate. In some embodiments the second gaseousreactant also comprises hydrogen plasma. In some embodiments the secondreactant is a mixture of H₂/N₂ plasma. In some embodiments the secondreactant is a nitrogen and hydrogen containing plasma created from aH₂/N₂ gas mixture which preferably has a H₂:N₂ ratio above 3:1, morepreferably above 4:1 and most preferably above 5:1. In some embodimentsH₂:N₂ ratios from about 5:1 to about 10:1 can be used. In someembodiments the second reactant is a nitrogen and hydrogen containingplasma created from H₂/N₂ gas mixture which preferably has a H₂:N₂ ratiobelow 3:1, more preferably below 5:2 and most preferably below 5:4. Insome embodiments H₂:N₂ ratios from about 1:4 to about 1:2 can be used.

Excess second reactant and gaseous byproducts of the surface reaction,if any, are removed from the reaction chamber, preferably by purgingwith the aid of an inert gas and/or evacuation. The InN depositioncycle, comprising the steps of pulsing and purging the first Inprecursor and the second N precursor, is repeated until a thin film ofInN of the desired thickness has been formed on the substrate, with eachcycle leaving no more than a molecular monolayer. Additional phasescomprising provision of a reactant and purging of the reaction space canbe included to form more complicated materials, such as ternarymaterials, as described in more detail below. Additional phases can alsobe used in some embodiments to enhance material properties such ascrystallinity.

As mentioned above, each pulse or phase of each cycle is preferablyself-limiting. An excess of reactant precursors is supplied in eachphase to saturate the susceptible structure surfaces. Surface saturationensures reactant occupation of all available reactive sites (subject,for example, to physical size or “steric hindrance” restraints) and thusensures excellent step coverage.

Removing excess reactants can include evacuating some of the contents ofthe reaction space and/or purging the reaction space with helium,nitrogen or another inert gas. In some embodiments purging can compriseturning off the flow of the reactive gas while continuing to flow aninert, carrier gas to the reaction space.

The precursors employed in the ALD type processes may be solid, liquidor gaseous materials under standard conditions (room temperature andatmospheric pressure), provided that the precursors are in vapor phasebefore they are conducted into the reaction chamber and contacted withthe substrate surface. “Pulsing” a vaporized precursor onto thesubstrate means that the precursor vapor is conducted into the chamberfor a limited period of time. Typically, the pulsing time is from about0.05 to 10 seconds. In some embodiments the pulsing time is from about0.05 s to about 1.0 s, preferably from about 0.1 s to about 0.5 s, morepreferably from about 0.1 s to about 0.3 s. However, depending on thesubstrate type and its surface area, and depending on the volume andshape of the reaction space, the pulsing time may be even higher than 10seconds. Pulsing times can be on the order of minutes in some cases. Theoptimum pulsing time can be determined by the skilled artisan based onthe particular circumstances.

The mass flow rate of the precursors can also be determined by theskilled artisan. In some single substrate chamber embodiments the flowrate of metal precursors is between about 1 and 1000 sccm withoutlimitation, more preferably between about 100 and 500 sccm.

The pressure in the reaction chamber is typically from about 0.01 toabout 20 mbar, more preferably from about 1 to about 10 mbar. However,in some cases the pressure will be higher or lower than this range, ascan be determined by the skilled artisan given the particularcircumstances. For example, during a purge step the pressure may bedecreased to a level of about 10⁻⁶ mbar by pumping down the reactionspace, for example, with the aid of turbo pump, if desired. During somepurge steps the pressure may vary from about 10⁻⁶ mbar to about 20 mbar.

Before starting the deposition of the film, the substrate is typicallyheated to a suitable growth temperature. The growth temperature variesdepending on the type of thin film formed, physical properties of theprecursors, etc. The growth temperatures are discussed in greater detailbelow in reference to each type of thin film formed. The growthtemperature can be less than the crystallization temperature for thedeposited materials such that an amorphous thin film is formed or it canbe above the crystallization temperature such that a crystalline thinfilm is formed. The preferred deposition temperature may vary dependingon a number of factors such as, and without limitation, the reactantprecursors, the pressure, flow rate, the arrangement of the reactor,crystallization temperature of the deposited thin film, and thecomposition of the substrate including the nature of the material onwhich deposition is to take place. The specific growth temperature maybe selected by the skilled artisan.

Although the In reactant is referred to as the first reactant and the Ncontaining reactant is referred to as the second reactant in thedescription above, the skilled artisan will recognize that in somesituations the N containing reactant may be provided first.

In some embodiments, the reactants and reaction by-products can beremoved from the reaction chamber by stopping the flow of the In or Nprecursor (or other precursor) while continuing the flow of an inertcarrier gas such as nitrogen or argon.

The growth rate of the InN containing thin film is generally less thanabout 2 angstroms per cycle, and may be less than 1.5 angstroms/cycle,less than about 1 angstrom/cycle, less than about 0.5 angstrom/cycle oreven less than about 0.3 angstrom/cycle in some cases.

As mentioned above, additional phases comprising provision of a reactantcan be included to form more complicated materials, such as ternarymaterials. In some embodiments the InN containing thin film may be dopedwith one or more additional dopant materials such as Ga, Al, Mg or P. Insome embodiments, a third reactant or dopant precursor comprising one ormore of these materials is provided at least once during each InNdeposition cycle. In some embodiments the dopant precursor may replacethe indium precursor in one or more deposition cycles. In otherembodiments, the dopant precursor is provided in addition to the indiumprecursor in one or more deposition cycles. In some embodiments thedopant precursor can be provided together with the indium precursor. Insome embodiments the dopant precursor can be provided separately fromthe indium precursor. The dopant precursor may be provided before orafter the indium precursor (e.g. 100 in FIG. 1A) and/or before or afterthe nitrogen precursor (e.g. 120 in FIG. 1A).

In other embodiments, one or more different deposition cycles may beprovided at a selected ratio with InN cycles to form a thin film withthe desired composition. The thin film may be a doped InN film, or maybe a nanolaminate film in which distinct layers of InN and one or moreadditional materials are formed. For example, a separate depositioncycle for forming a metal nitride such as AlN, GaN, or MgN, or otherfilm may be used. The InN deposition cycle is carried out at a desiredratio to the other deposition cycle in order to obtain the desiredcomposition in the InN film. The indium content can be expressed (usingAlN as an example) as a percentage of the overall metal content in thefilm, e.g. In/(In+Al). In some embodiments the In/(In+Al) ratio in thedeposited film is about 0-20% and preferably about 0-50%. In someembodiments the In/(In+Al) ratio in the deposited film is up to about100%. Since growth is by ALD and therefore self-limited and independentof small temperature variations, a uniform composition, for example Ga,Mg, or Al, across the substrate surface can be obtained. The ratio ofInN deposition cycles to other metal nitride deposition cycles or otherdeposition cycles can be selected such that a desired composition isachieved. In some embodiments the ratio of InN deposition cycles to InNplus other deposition cycles is less than about 0.5. In some embodimentsthe ratio of InN deposition cycles to InN plus other deposition cyclesis less than about 0.4, preferably less than about 0.3, more preferablyless than about 0.2, and in some cases less than about 0.1. In someembodiments, multiple cycles of InN are performed followed by multiplecycles of the other deposition cycle to form a nanolaminate film of InNand another material.

Excess second reactant and gaseous byproducts of the surface reaction,if any, are removed from the reaction chamber, preferably by purgingwith the aid of an inert gas and/or evacuation. The InN depositioncycle, comprising the steps of pulsing and purging the first Inprecursor and the second N precursor, is repeated until a thin film ofInN of the desired thickness has been formed on the substrate, with eachcycle leaving no more than a molecular monolayer. The InN and the AlNdeposition cycle are repeated at an appropriate ratio to produce anInAlN film with the desired composition. For example, to achieve an Inconcentration of about 20-at %, 12 cycles of InN can be mixed with threecycles of AlN deposition. In some embodiments, an InAlN film comprisinggreater than about 30-at % In is deposited. Since growth is by ALD andtherefore self-limited and relatively independent of small temperaturevariations, a uniform amount of doping across the substrate is obtained.

As mentioned above, in some embodiments InN is provided at a specifiedratio with AlN. An AlN deposition cycle is similar to the InN depositioncycles described above. Thus, in some embodiments an AlN depositioncycle comprises providing a first aluminum precursor into the reactionchamber in the form of a vapor phase pulse such that it contacts thesurface of the substrate. Conditions are preferably selected such thatno more than about one monolayer of the first Al reactant is adsorbed onthe substrate surface in a self-limiting manner. The appropriate pulsingtimes can be readily determined by the skilled artisan based on theparticular circumstances. In some embodiments, pulsing times are fromabout 0.05 to 10 seconds. Example 8 provides an example of a suitableAlN deposition cycle. In some embodiments, where AlN can be deposited,preferably separately from the other materials, the reaction temperaturefor the AlN deposition is preferably less than 120° C., more preferablyless than 100° C. and most preferably less than 50° C. In some cases theAlN is deposited at room temperature i.e. from about 20° C. to 25° C.

In some embodiments the Al reactant is an Al halide, such as AlCl₃ orAlI₃. In other embodiments the Al reactant may be an organic Alprecursor, such as trimethylaluminum (TMA). The organic Al precursor mayhave the formula AlR₃, wherein the R is selected from substituted,branched, linear or cyclic C1-C10 hydrocarbons. In some embodiments 0-3of the R groups are methyl and the rest are ethyl. In some embodiments,the Al precursors has both a halide ligand and organic ligand, forexample AlR_(x)X_(3-x), wherein x is from 1 to 2 and R is organicligand, such as alkyl or alkenyl and X is halide, such as chloride.Examples of this kind of In precursors might be, for example,dimethylaluminumchloride (CH₃)₂AlCl.

Excess first reactant and reaction byproducts, if any, are removed fromthe reaction chamber, such as by purging with an inert gas and a secondgaseous reactant comprising N is pulsed into the chamber where it reactswith the first Al reactant bound to the surface. The nitrogen precursormay be, for example, NH₃ or N₂H₄. In some embodiments the N precursorcomprises nitrogen plasma.

Excess second reactant and gaseous byproducts of the surface reaction,if any, are removed from the reaction chamber, preferably by purgingwith the aid of an inert gas and/or evacuation. The AlN depositioncycle, comprising the steps of pulsing and purging the first Alprecursor and the second N precursor, is repeated until a thin film ofAlN of the desired thickness has been formed on the substrate, with eachcycle leaving no more than a molecular monolayer. The AlN and the InNdeposition cycle are repeated at an appropriate ratio to produce anAlInN film with the desired composition.

In other embodiments, a single In or Al reactant is used in an ALDprocess, where the single reactant comprises nitrogen and In or Al. Insome embodiments plasma can be used with the single reactant, includinghydrogen plasma, plasma generated from a mixture of hydrogen andnitrogen, and NH₃ plasma.

As mentioned above, in some embodiments InN is provided at a specifiedratio with GaN to deposit a film with a desired composition. A GaNdeposition cycle similar to the InN deposition cycles described abovecan be used. For example, FIG. 1B is a flow chart generally illustratinga method for forming a GaN film in accordance with one embodiment. Thesubstrate is contacted with a Ga precursor 200 followed by removing anyexcess reactant 210. The substrate is then contacted with a nitrogenprecursor 220 followed by removing any excess reactant 230. Thecontacting steps are repeated until a film of a desired thickness isformed 240. In some embodiments an GaN deposition cycle comprisesproviding a first gallium precursor into the reaction chamber in theform of a vapor phase pulse such that it contacts the surface of thesubstrate. Conditions are preferably selected such that no more thanabout one monolayer of the first Ga reactant is adsorbed on thesubstrate surface in a self-limiting manner. The appropriate pulsingtimes can be readily determined by the skilled artisan based on theparticular circumstances. In some embodiments, pulsing times are fromabout 0.05 to 10 seconds.

In some embodiments the Ga reactant is a Ga halide, such as GaCl₃, GaClor GaI₃. In other embodiments the Ga reactant may be a metalorganic ororganometallic Ga precursor, such as trimethylgallium (TMG) ortriethylgallium (TEG). The organic Ga precursor may have the formulaGaR₃, wherein the R is selected from substituted, branched, linear orcyclic C1-C10 hydrocarbons. In some embodiments 0-3 of the R groups aremethyl and the rest are ethyl.

In some embodiments, each deposition cycle includes a further plasmaprocessing step in which the substrate is contacted with a plasma tofurther facilitate film crystallization by increasing surface mobilitywith the heat generated by radical recombination on the surface. Inother embodiments, a further plasma processing step is provided once athin film of a desired thickness has been deposited, or at intervalsduring the deposition process. In some embodiments the plasma isprovided in each cycle. In other embodiments the plasma is provided onceevery 10 to 20 cycles and is generated from nitrogen and/or hydrogen.

Thermal Atomic Layer Deposition of InN

In some embodiments no plasma or activated species is used in the InNALD cycles. In some embodiments the thermal ALD InN cycles can be usedin combination with one or more plasma ALD cycles for depositing anothermaterial or additional metal nitride.

In some embodiments, an evaporation temperature for the In reactant maybe from about 180° C. to about 220° C. The deposition temperature ispreferably below about 800° C., below about 700° C., below about 600°C., below about 550° C., below about 500° C., below about 450° C., orbelow about 400° C. The reaction chamber may be part of a flow-typereactor. In some embodiments the deposited film is an epitaxial orsingle-crystal film.

The In reactant may be an In halide, such as InCl₃ or InI₃ and thesecond reactant may be a nitrogen containing reactant such as NH₃ orN₂H₄. The temperature of the process is preferably below about 800° C.,below about 700° C., below about 600° C., below about 500° C. or belowabout 400° C. The reaction chamber may be part of a flow-type reactor.In some embodiments the deposited film is an epitaxial or single-crystalfilm.

In other embodiments, a thermal ALD process uses an organic Inprecursor, such as cyclopentadienylindium (InCp), dimethylethylindium(DMEI), trimethylindium (TMI) or triethylindium (TEI). In someembodiments, the organic In precursor has the formula InR₃, wherein theR is selected from the group consisting of substituted, branched, linearand cyclic C1-C10 hydrocarbons. In some embodiments reactants areevaporated at room temperature. The second reactant may be a nitrogencontaining reactant such as NH₃ or N₂H₄. The deposition temperature ofthe process is preferably selected such that the In reactant does notdecompose, for example below about 400° C. or below about 300° C.,depending on the particular reactant employed. The reaction chamber maybe part of a flow-type reactor. In some embodiments the deposited filmis an epitaxial or single-crystal film.

Plasma Enhanced Atomic Layer Deposition of InN

In other embodiments, a plasma ALD process is used to deposit an InNcontaining thin film. In some such embodiments, the In precursor may be,for example, an In halide precursor, such as InCl₃ or InI₃. Theevaporation temperature for the In reactant may be from about 180° C. toabout 220° C. in some embodiments. The second reactant comprising N maybe a nitrogen plasma containing precursor. In some embodiments thenitrogen plasma is generated in situ, for example above or directly inview of the substrate. In other embodiments the nitrogen plasma isformed remotely, for example upstream of the substrate. In some suchembodiments, the nitrogen plasma does not have a substantial amount of Nions, and is primarily N atoms. In some embodiments the second reactantalso comprises hydrogen plasma. In some embodiments the second reactantis a mixture of H₂/N₂ plasma. In some embodiments the second reactant isa nitrogen and hydrogen containing plasma created from a H₂/N₂ gasmixture which preferably has a H₂:N₂ ratio above 3:1, more preferablyabove 4:1 and most preferably above 5:1. In some embodiments H₂/N₂ratios from about 5:1 to about 10:1 can be used. In some embodiments theratio of hydrogen to nitrogen can be selected to deposit a film havingdesired properties, such as density, roughness, crystallinity, andcomposition. The reaction temperature may be, for example, less thanabout 500° C., less than about 400° C., less than about 300° C., lessthan about 250° C., or even less than about 200° C. The process may beperformed in a flow-type reactor. In some embodiments the deposited filmis an epitaxial or single-crystal film.

The In reactant may be an organic In precursor, such ascyclopentadienylindium (InCp), dimethylethylindium (DMEI),trimethylindium (TMI) or triethylindium (TEI), and the second reactantmay be a nitrogen containing plasma, and may comprise atomic nitrogen ornitrogen radicals, and may be made for example, from NH₃ or N₂/H₂mixture. The temperature of the process is preferably below about 500°C., below about 400° C., below about 300° C., below about 250° C. orbelow about 200° C. The reaction chamber may be part of a flow-typereactor. In some embodiments the deposited film is an epitaxial orsingle-crystal film.

In other plasma ALD processes an organic In reactant is used, such asdimethylethylindium (DMEI), trimethylindium (TMI) or triethylindium(TEI). In some embodiments, the organic In precursor has the formulaInR₃, wherein the R is selected from the group consisting ofsubstituted, branched, linear and cyclic C1-C10 hydrocarbons. The Inprecursor may be evaporated at room temperature. The second reactantcomprising N may be a nitrogen plasma containing precursor. In someembodiments the nitrogen plasma is generated in situ, for example aboveor directly in view of the substrate. In other embodiments the nitrogenplasma is formed remotely, for example upstream of the substrate. Insome such embodiments, the nitrogen plasma does not have a substantialamount of N ions, and is primarily N atoms. In some embodiments thesecond reactant also comprises hydrogen plasma. In some embodiments thesecond reactant is a mixture of H₂/N₂ plasma. The reaction temperatureis generally chosen such that the In precursor does not decompose andmay be, for example, less than about 400° C., less than about 300° C. oreven less than about 200° C., depending on the precursor. The processmay be performed in a flow-type reactor. In some embodiments thedeposited film is an epitaxial or single-crystal film.

In some embodiments the plasma power can be varied. Preferably theplasma power supplied is about 100 W or more. In some embodiments theplasma power is greater than about 200 W, preferably greater than about300 W, more preferably greater than about 400 W, and in some cases aboveabout 500 W or 600 W. In some embodiments the plasma parameters can beselected to achieve desired properties in the deposited film, such asthe film thickness, roughness, and density.

In some embodiments the reaction conditions can be selected to deposit afilm with a desired density. In some embodiments the density is greaterthan about 3 g/cm³. In some embodiments the density is greater thanabout 4.5 g/cm³. In some embodiments the density of the deposited filmis greater than about 5 g/cm³. In some embodiments the density of thedeposited film is greater than about 5.5 g/cm³

In some embodiments the reaction conditions can be selected to deposit afilm with a desired roughness or smoothness. In some embodiments theroughness is less than about 4 nm. In some embodiments the roughness isless than about 3 nm. In some embodiments the roughness of the depositedfilm is preferably less than about 2 nm. In some embodiments theroughness of the deposited film is preferably less than about 1.5 nm.

In some embodiments the plasma ALD InN cycles can be used with thermalALD cycles for depositing another material or additional metal nitride.

Example 1

InGaN thin films were deposited using 1000 deposition cycles. InN andGaN deposition cycles were used. The ratio between the InN and GaNdeposition cycles was varied. The substrate temperature was 200° C.during the film deposition. TEG and nitrogen plasma were used for theGaN deposition cycles. TMI and nitrogen plasma were used for the InNdeposition cycles. The plasma power supplied was 400 W.

FIG. 2A shows the growth rate for the deposited films for variousInN/(InN+GaN) ratios. The growth rate was between about 0.3 and 0.5 Åper cycle.

FIG. 2B shows the In/(In+Ga) content as measured by EDX for thedeposited films for various InN/(InN+GaN) ratios. The indium content inthe films increased with an increased InN/(InN+GaN) ratio.

Example 2

InGaN films were deposited with various hydrogen:nitrogen ratios. TheInGaN thin films were deposited using 1000 deposition cycles. InN andGaN deposition cycles were used. The substrate temperature was 200° C.during the film deposition. TMG and a mixture of hydrogen/nitrogenplasma were used for the GaN deposition cycles. TMI and a mixture ofhydrogen/nitrogen plasma were used for the InN deposition cycles. Theplasma power supplied was 400 W. The ratio between the hydrogen andnitrogen gases was varied. FIGS. 3A-3C illustrate the thickness,roughness, and density for the deposited InGaN films. FIG. 3A shows thatthe thickness of the deposited film decreased as the hydrogen:nitrogenratio increased. FIG. 3B shows that the roughness of the deposited filmincreased as the hydrogen:nitrogen ratio was increased. FIG. 3C showsthat the highest film density was achieved using a hydrogen:nitrogenratio of about 1.

Example 3

InGaN thin films were deposited using 1000 deposition cycles whilevarying the plasma power. FIGS. 4A-4C illustrate the thickness,roughness, and density for the deposited InGaN films. FIG. 4A shows thatthe thickness of the deposited film increased as the plasma powerincreased. FIG. 4B shows that the roughness of the deposited filmincreased as the plasma power increased. FIG. 4C shows that the densityof the deposited film decreased with a plasma power of about 500 W orgreater.

Example 4

FIG. 5 shows the growth rate while varying the supply of galliumreactant to the reaction space. The supply of gallium reactant wasvaried by turning the needle valve that controlled the flow of reactant.The growth of GaN saturated after about 4 turns of the needle valve,thus illustrating that growth rate increases with increasing flow rateof gallium reactant up to a point, beyond which saturation occurs ineach cycle.

Example 5

FIGS. 6A-6C show glancing incidence x-ray diffraction (GIXRD) graphs forvarious 20 values. FIG. 6A is an InGaN thin film deposited on sapphire.The largest peak in FIG. 6A corresponds to the (006) peak of sapphirewith a smaller (002) peak. FIG. 6B is a GaN thin film deposited onsapphire. The largest peak in FIG. 6B corresponds to the (006) peak ofsapphire with a smaller (002) peak. FIG. 6C shows a portion of the GIXRDdata from 6A. The rocking curve of (002) has a FWHM (Full Width at HalfMaximum) of 8.3° on sapphire.

Example 6

FIG. 7 shows temperature versus 20 values with brighter/lighter areasindicating increased counts for the x-ray diffraction pattern. The peakvalue was around 33-34.6°, with increased temperature shifting the peakcloser to the expected 34.6° value for GaN (002).

Example 7

InN thin films were deposited using trimethylindium (TMI) and NH₃-plasmaas precursors. The substrate temperature was 200° C. during the filmdeposition. The deposition resulted in 0.5 Å/cycle growth rate and arefractive index of 1.9-2.0 in the deposited film. The cycle time was 6seconds. 400 W plasma power was used and 50 sccm NH₃ flow was usedduring the plasma exposure.

Example 8

AlN thin films were deposited using an AlN cycle includingtrimethylaluminum (TMA) and NH₃-plasma. The substrate temperature was atroom temperature i.e. about 20° C. during the film deposition. The filmgrew at a high rate, approximately 2.0 Å/cycle. The resulting film had arefractive index of 1.55. The cycle time was 6 seconds.

It will be appreciated by those skilled in the art that variousmodifications and changes can be made without departing from the scopeof the invention. Similar other modifications and changes are intendedto fall within the scope of the invention, as defined by the appendedclaims.

We claim:
 1. A method for depositing a thin film comprising InN on asubstrate in a reaction space by an atomic layer deposition processcomprising a plurality of InN deposition cycles, each deposition cyclecomprising: contacting the substrate with a In precursor such that nomore than a single monolayer of the In precursor adsorbs on thesubstrate surface in a self-limiting manner; and contacting thesubstrate with a nitrogen precursor comprising a nitrogen (N) plasma,such that the nitrogen precursor reacts with the adsorbed In precursorto form InN, wherein the reaction space is part of a flow-type reactor.2. The method of claim 1, wherein the deposited thin film is epitaxialor single-crystal film.
 3. The method of claim 1, wherein the InN isdeposited at a growth rate of less than 1.5 Å/deposition cycle.
 4. Themethod of claim 1, wherein the InN is deposited at a growth rate of lessthan 1 Å/deposition cycle.
 5. The method of claim 1, wherein the InN isdeposited at a growth rate of less than 0.5 Å/deposition cycle.
 6. Themethod of claim 1, wherein the deposition cycle additionally comprisescontacting the substrate with a plasma pulse to provide heat forcrystallization.
 7. The method of claim 1, wherein the In precursor isan organic In compound.
 8. The method of claim 7, wherein the organic Incompound is cyclopentadienylindium (InCp), dimethylethylindium (DMEI),trimethylindium (TMI) or triethylindium (TEI).
 9. The method of claim 7,wherein the organic In compound has a formula InR₃, wherein the R isselected from substituted, branched, linear or cyclic C1-C10hydrocarbons.
 10. The method of claim 1, further comprising a GaNdeposition cycle thereby depositing a GaInN film.
 11. An atomic layerdeposition (ALD) process for forming an InN containing thin film on asubstrate in a reaction chamber comprising a plurality of InN depositioncycles, each cycle comprising: providing a pulse of a first vapor phaseIn halide reactant into the reaction chamber to form no more than abouta single molecular layer of the first reactant on the substrate;removing excess first reactant from the reaction chamber; providing apulse of a second vapor phase N reactant to the reaction chamber suchthat the second vapor phase reactant reacts with the first reactant onthe substrate to form InN, wherein the second vapor phase N reactantcomprises N plasma; and removing excess second reactant and reactionbyproducts, if any, from the reaction chamber.
 12. The method of claim11, wherein the InN thin film is deposited at a temperature below 800°C.
 13. The method of claim 11, wherein the InN thin film is deposited ata temperature below 400° C.
 14. The method of claim 11, wherein thereaction chamber is part of a flow-type reactor.
 15. The method of claim11, wherein the deposited InN thin film is an epitaxial orsingle-crystal film.
 16. An atomic layer deposition (ALD) process forforming an InN containing thin film on a substrate in a reaction chambercomprising a plurality of InN deposition cycles, each cycle comprising:providing a pulse of a first vapor phase in halide reactant into thereaction chamber to form no more than about a single molecular layer ofthe first reactant on the substrate; removing excess first reactant fromthe reaction chamber; providing a puke of a second reactant comprisingnitrogen plasma to the reaction chamber such that the second reactantreacts with the first reactant on the substrate to form InN, andremoving excess second reactant and reaction byproducts, if any, fromthe reaction chamber.
 17. The method of claim 16, wherein the Inprecursor is InCl₃ or InI₃.
 18. The method of claim 16, wherein thenitrogen plasma is formed in situ.
 19. The method of claim 16, whereinthe nitrogen plasma is formed remotely.
 20. The method of claim 16,wherein the nitrogen plasma does not have substantial amount of N ionswhen it contacts the substrate.
 21. The method of claim 16, wherein thesecond reactant further comprises hydrogen plasma.
 22. The method ofclaim 16, wherein the InN thin film is deposited at a temperature below500° C.
 23. An atomic layer deposition (ALD) process for forming an InNcontaining thin film on a substrate in a reaction chamber comprising aplurality of deposition cycles, each cycle comprising: providing a pulseof a first organic In precursor into the reaction chamber to form nomore than about a single molecular layer of the first reactant on thesubstrate; removing excess first reactant from the reaction chamber;providing a pulse of a second reactant comprising N plasma to thereaction chamber such that the second reactant reacts with the firstreactant on the substrate to form InN, and removing excess secondreactant and reaction byproducts, if any, from the reaction chamber. 24.The method of claim 23, wherein the InN thin film is deposited at atemperature below 400° C.
 25. The method of claim 23, wherein the InNthin film is deposited at a temperature below 200° C.
 26. The method ofclaim 23, wherein the ALD process is carried out at a temperature atwhich the In precursor does not decompose.